Process for the production of sucrose esters of fatty acids



United States Patent 10 Claims. (Cl. 260-234) This invention relates toa process for the production of sucrose esters of fatty acids.

Sucrose esters of fatty acids are known and are commercially used asemulsifier-s. More recently, chiefly the sucrose esters of fatty acidshaving from 12 to 22 carbon atoms and at least one weakly hydrophilicgroup in the fatty acid chain have gained importance because they arecharacterized by outstanding detergency characteristics and are readilydegraded biologically to absolutely innoxious substances (German patentapplication Z 10,316).

Sucrose esters of fatty acids are conventionally prepared bytransesterification of lower alkyl esters of fatty acids with sucrose ina polar solvent (see British Patents 809,815 and 826,801), the molarratio of fatty acid alkyl ester to sucrose being about 3:1 and more.Suitable catalysts include above all alkaline compounds, especiallypotassium carbonate. After completion of the transesterification, thepredominant part of the solvent is removed under vacuum. Then adifferent suitable solvent must be added to prevent decomposition of thesucrose esters by excessively long heating and to precipitate excesssugar. The resultant solution of the sucrose ester must still be washed,and the sucrose ester is left in pure form after evaporation of theextractant.

This process has the disadvantage, above all when carried out in acommercial scale, that it is extremely complicated and requires a greatexcess of sucrose and large amounts of the polar solvent. Both theexcess sucrose and the solvent must be recovered and re-used to make theprocess economic. This in turn requires additional purificationprocedures for both substances with the corresponding expense ofequipment.

It is an object of the present invention to provide an improved processfor the production of sucrose esters of fatty acids having from 12 to 22carbon atoms, which comprises effecting the transesterification ofsucrose with a lower fatty acid alkyl ester in a liquid two-phasesystem, one phase of which consists at the beginning of the reaction ofa solution of the fatty acid alkyl ester in an aliphatic or aromatichydrocarbon, and the other phase of which comprises sucrose and, ifnecessary or desired, the catalyst dissolved in a polar solvent.

Suitable polar solvents which may be used for the purposes of theinvention are N-rnethyl morpholine, triethylamine, pyridine, quinoline,pyrazine, N-methylpyrazine, N,N-dimethyl-pyrazine, 2-pyrrolidone, N-methyl-pyrrolidone as well as N,N'-dimethyl formamide and dimethylsulfoxide which are particularly preferred. Suitable solvents for thelower alkyl esters of fatty acids are non-polar solvents boiling between100 C. and 200 C., particularly suitable being aromatic and aliphatichydrocarbons such as toluene, ethyl benzene, gasoline, cyclohexylbenzene, nonyl benzene, ligroin and the like. The ratio by weight ofpolar solvent to the liquid hydrocarbon is desirably 0.5:1 to 5:1,especially 2:1 to 2.5:].

The process of the invention is generally applicable to the productionof sucrose esters of fatty acids. It has been found to be particularlyadvantageous for the production of the commercially important sucroseesters of fatty acids containing at least one weakly hydrophilic groupsuch as a hydroxyl, carbonyl, oxime or alkoxy group.

The principle of the process consists in that the sucrose and thecatalyst are initially dissolved at moderately elevated temperature of,for example, 70 to 90 C. in the polar solvent. Then the lower alkylester of the fatty acid the sucrose ester of which is desired to beprepared, especially the methyl or ethyl ester, is dissolved in theliquid hydrocarbon and the two phases are reacted at temperatures ofbetween 40 and 180 C., especially about to C., while stirring.Initially, the alkyl ester remains almost completely in the hydrocarbonphase. The lower alcohol liberated during the transesterificationdistils and, at the same time, the dissolving power of the polar solventfor the hydrocarbon increases because the sucrose ester which is formedis better soluble in the polar solvent than the sucrose. After areaction period of 5 to 12 hours and in general of about 8 to 9 hours,the transesterification is completed, and the two solvents are distilledoff by increasing the temperature in the reaction mixture or the vaccumapplied or by both of these measures and the sucrose ester producedremains in the residue.

The new process has the following advantages from the processengineering and economic points of view as compared with known methods:Sucrose and the lower alkyl ester of fatty acid may be fed in a molarratio of 1:1. Thus, the process is not burdened by excess sugar, and theseparation and purification of excess sucrose are eliminated. The totalamount of solvent necessary for the transesterification is less thanone-half of the quantity previously used. The yield of sucrose ester isincreased by about 10% on an average due to the substantially moresimple processing and elimination of all additional purificationprocedures.

EXAMPLE 1 Sucrose in an amount of 51.5 gms. (0.15 mole) was dissolvedwith 0.5 gm. of potassium carbonate in 120 gms. of dimethyl sulfoxide at85 C. At the same time, a solution of 0.15 mole of 12-hydroxymethylstearate in 50 gms. of cyclohexyl benzene was prepared and the twophases were then vigorously stirred for 9 hours at 85 C. under vacuum.Then the two solvents were distilled off under vacuum. The residueconsisted of the sucrose ester of 12-hydroxystearic acid. The yield ismore than The product may be used directly as such as the activedetergent component of detergent compositions and lowers the surfacetension of water of 10 deg. German hardness to 38 dynes/ cm.

EXAMPLE 2 A mixture of 90 gms. of dimethyl sulfoxide, 50 gms. ofgasoline boiling from to C., 30 gms. of sucrose, 27.6 gms. of12-hydroxymethyl stearate and 0.5 gm. of potassium carbonate catalyst isvigorously stirred for 9 hours at 85 C. under a vacuum of 100 mm. Hg.After having distilled off the solvents, there remains sucrose-12-hydroxystearate having a surface tension of 38 dynes/ cm. The yieldis 96%.

Corresponding yields are obtained when transesterifying myristic acid orlauric acid methyl ester with sucrose.

What is claimed is:

l. A process for the production of sucrose mono-esters of fatty acidshaving from 12 to 22 carbon atoms by transesterification of sucrose witha lower alkyl ester of a fatty acid in inert solvents, which comprises(1) forming a liquid two-phase system, a first phase of this systemconsisting of a solution of said fatty acid alkyl ester in an aliphaticor aromatic hydrocarbon non-polar solvent having a boiling point above100 C., and a second phase of this system containing said sucrose andpotassium carbonate catalyst dissolved in a polar solvent at from 70-90C., said sucrose and said lower alkyl ester of a fatty acid beingpresent in about a 1:1 mole ratio, (2) stirring the said two phases at atemperature of between 40180 C. while distilling oif lower alcoholliberated by the transesterification reaction, and (3) distilling offthe remaining solvents.

2. The process of claim 1, wherein the ratio by weight of said polarsolvent to said non-polar solvent is from 0.521 to 5:1.

3. The process of claim 2, wherein the ratio by weight of said polarsolvent to said non-polar solvent is from 2:1 to 25:1.

4. The process of claim 1, wherein said fatty acid alkyl ester is thealkyl ester of a fatty acid having at least one weakly hydrophilic groupin the fatty acid chain.

5. The process of claim 1, wherein said polar solvent is dimethylsulfoxide.

6. The process of claim 1, wherein said polar solvent is dimethylformamide.

7. The process of claim 4, wherein said weakly hydrophilic group in thefatty acid chain is a hydroxyl, a carbonyl, an oxime or an alkoxy group.

References Cited UNITED STATES PATENTS 2,948,716 8/1960 Davis 2602343,054,789 9/1962 DAmato 260234 3,251,829 5/1966 Hagge et a1. 260-234FOREIGN PATENTS 826,801 1/ 1960 Great Britain. 859,305 1/1961 GreatBritain.

LEWIS GOTTS, Primary Examiner.

JAMES O. THOMAS, 111., Examiner.

J. R. BROWN, Assistant Examiner.

1. A PROCESS FOR THE PRODUCTION OF SUCROSE MONO-ESTERS OF FATTY ACIDSHAVING FROM 12 TO 22 CARBON ATOMS BY TRANSESTERIFICATION OF SUCROSE WITHA LOWER ALKYL ESTER OF A FATTY ACID IN INERT SOLVENTS, WHICH COMPRISES(1) FORMING A LIQUID TWO-PHASE SYSTEM, A FIRST PHASE OF THIS SYSTEMCONSISTING OF A SOLUTION OF SAID FATTY ACID ALKYL ESTER IN AN ALIPHATICOR AROMATIC HYDROCARBON NON-POLAR SOLVENT HAVING A BOILING POINT ABOVE100*C., AND A SECOND PHASE OF THIS SYSTEM CONTAINING SAID SUCROSE ANDPOTASSIUM CARBONATE CATALYST DISSOLVED IN A POLAR SOLVENT AT FROM70-90*C., SAID SUCROSE AND SAID LOWER ALKYL ESTER OF A FATTY ACID BEINGPRESENT IN ABOUT A 1:1 MOLE RATIO, (2) STIRRING THE SAID TWO PHASES AT ATEMPERATURE OF BETWEEN 40-180*C. WHILE DISTILLING OFF LOWER ALCOHOLLIBERATED BY THE TRANSESTERIFICATION REACTION, AND (3) DISTILLING OFFTHE REMAINING SOLVENTS.